Stabilized lithium metal impressions coated with alloy-forming elements and method for production thereof

ABSTRACT

The invention relates to particulate lithium metal composite materials, stabilized by alloy-forming elements of the third and fourth primary group of the PSE and method for production thereof by reaction of lithium metal with film-forming element precursors of the general formulas (I) or (II): [AR 1 R 2 R 3 R 4 ]Li x  (I), or R 1 R 2 R 3 A-O-AR 4 R 5 R 6  (II), wherein: R 1 R 2 R 3 R 4 R 5 R 6 =alkyl (C 1 -C 12 ), aryl, alkoxy, aryloxy-, or halogen (F, Cl, Br, I), independently of each other; or two groups R represent together a 1,2-diolate (1,2-ethandiolate, for example), a 1,2- or 1,3-dicarboxylate (oxalate or malonate, for example) or a 2-hydroxycarboxylate dianion (lactate or salicylate, for example); the groups R 1  to R 6  can comprise additional functional groups, such as alkoxy groups; A=boron, aluminum, gallium, indium, thallium, silicon, germanium, tin, lead; x=0 or 1 for B, Al, Ga, In, Tl; x=0 for Si, Ge, Sn, Pb; in the case that x=0 and A=B, Al, Ga, In, Tl, R 4  is omitted, or with polymers comprising one or more of the elements B, Al, Ga, In, Tl, Si, Ge, Sn, Pb, at temperatures between 50 and 300° C., preferably above the melting temperature of lithium of 180.5° C., in an organic, inert solvent.

The invention relates to particulate metal composite materialsstabilized with alloy-forming elements of main groups 3 and 4 of theperiodic table of elements as well as a method for producing the same byreacting lithium metal with film-forming element precursors in anorganic inert solvent at temperatures between 50° C. and 300° C.,preferably above the melting point of lithium.

Lithium is one of the alkali metals. Like the heavy element homologs ofthe first main group, lithium is characterized by a strong reactivitywith a variety of substances. It thus reacts violently with water,alcohols and other substances containing protic hydrogen, often withignition. It is unstable in air and reacts with oxygen, nitrogen andcarbon dioxide. It is therefore normally handled under an inert gas(noble gases such as argon) and is stored under a protective layer ofparaffin oil.

Lithium also reacts with many functionalized solvents, even if they donot contain protic hydrogen. For example, cyclic ethers such as THF areopened by ring cleavage, esters and carbonyl compounds are lithiatedand/or reduced in general. The reaction between the aforementionedchemicals and/or environmental substances is often catalyzed by water.Lithium metal can therefore be stored and processed in dry air for longperiods of time because it forms a somewhat stable passivation layerthat prevents most corrosion. This is also true of functionalizedsolvents, for example, N-methyl-2-pyrrolidone (NMP), which is much lessreactive with lithium in anhydrous form than lithium with a watercontent of more than a few 100 ppm.

To increase safety in processing and the stability of lithium metal instorage, a number of corrosion-preventing coating methods have beendeveloped. For example, it is known from U.S. Pat. No. 5,567,474 andU.S. Pat. No. 5,776,369 that molten lithium metal may be treated withCO₂. For the coating, molten lithium in an inert hydrocarbon istypically brought in contact with at least 0.3% CO₂ for at least oneminute. However, the resulting protection is not sufficient for manyapplications, specifically for prelithiation of battery electrodematerials in N-methyl-2-pyrrolidone (NMP) suspension.

Another method for stabilizing lithium metal consists of heating itabove its melting point, agitating the molten lithium and bringing it incontact with a fluorination agent, for example, perfluoropentylamine (WO2007/005983 A2). It is a disadvantage that fluorinating agents are oftentoxic or caustic and therefore tend to be avoided in industrialpractice.

Another method of protective surface treatment of lithium metal consistsof coating it with a wax layer, for example, a polyethylene wax (WO2008/045557 A1). It is a disadvantage that a relatively large amount ofcoating agent must be applied. This amount is approx. 1% in the examplesin the patent application cited above.

US 2008/0283155 A1 describes a method for stabilizing lithium metal,which is characterized by the following steps:

a) Heating lithium metal powder to a temperature above the melting pointto produce molten lithium metal,

b) Dispersing the molten lithium metal, and

c) Bringing the molten lithium metal in contact with a substance thatcontains phosphorus to produce an essentially continuous protectivelayer of lithium phosphate on the lithium metal powder. It is adisadvantage to handle acidic caustic substances (phosphoric acid) ingeneral and in particular in the presence of lithium metal: these twosubstances react very violently with one another when brought in contactand release a substantial amount of heat. In addition, the reaction oflithium metal with phosphoric acid produces hydrogen gas, which isexplosive.

US 2009/0061321 A1 proposes the production of a stabilized lithium metalpowder having an essentially continuous polymer coating. The polymer maybe selected from the group of polyurethanes, PTFE, PVC, polystyrene,etc. One disadvantage of this method is that the protected lithium metalhas an undefined surface coating of organic substances which caninterfere in its subsequent use, for example, for prelithiation ofelectrode materials.

Finally, an anode for an electrochemical cell containing a metallicmaterial with an oxygen-based coating, is formed with a (additional)protective layer which is formed by reaction of D- or P-block precursorswith this layer containing oxygen (WO 2010/101856 A1, US 2007/0082268A1, US 2009/0220857 A1). The protective layer of the metal anodematerial is produced by treating a metallic material, which has acoating that contains oxygen, with at least two compounds, wherein thefirst compound is a large molecular compound and the second compound isa small molecular compound (U.S. Pat. No. 7,776,385 B2, US 2011/0104366A1). With this type of protective layer formation, surface groups thatcontain oxygen (for example, hydroxyl functions) will react with D- orP-block precursors, for example, a silicic acid ester, in anonhydrolytic sol-gel process, forming a film consisting of SiO₂ on theanode surface. These chemical reactions can be formulated as follows (G.A. Umeda et al., J. Mater. Chem. 2011, 21, 1593-1599):

LiOH+Si(OR)₄→LiOSi(OR)₃+ROH

SiOR+ROSi→Si—O—Si+ROR

One disadvantage of this method is that it takes place in multiplesteps, i.e., first the metallic material, for example, lithium metal, isprovided with a layer containing oxygen and then is reacted with twodifferent molecular compounds (D- or P-block precursors).

The object of the invention is to provide lithium metal impressions witha passivating top coat as well as a method for producing these metalimpressions,

-   -   which do not require the use of gaseous or acidic, caustic or        toxic passivating agents,    -   which cause the formation of a passivating protective layer        consisting of a mixed organic/inorganic sparingly soluble film        on the lithium surface, and    -   whose surface coating does not interfere during use as a        prelithiating agent for anode materials, for example, and    -   which contain in the surface layer elements having an affinity        for the binders conventionally used.

Such lithium metal impressions should be stable for several days attemperatures up to at least about 50° C. in the presence of polarreactive solvents such as those used for the production of electrodecoatings, i.e., NMP, for example.

According to the invention, the object is achieved by the fact that thelithium metal impression contains a core of metallic lithium, which issurrounded with an outer layer containing one or more elements of maingroups 3 and/or 4 of the periodic table of elements that can be alloyedwith lithium. The lithium metal impressions according to the inventionare produced by bringing them in contact with one or more passivatingagents of general formulas I or II:

[AR¹R²R³R⁴]Li_(x)  (I)

or R¹R²R³A-O-AR⁴R⁵R⁶  (II)

wherein

-   -   R¹R²R³R⁴R⁵R⁶=independently of one another alkyl (C₁-C₁₂), aryl,        alkoxy, aryloxy or halogen (F, Cl, Br, I) or two radicals R        together denote a 1,2-diolate (for example, 1,2-ethanediolate),        a 1,2- or 1,3-dicarboxylate (for example, oxalate or malonate)        or a 2-hydroxycarboxylate dianion (for example, glycolate,        lactate or salicylate);    -   radicals R¹ to R⁶ may contain additional functional groups, for        example, alkoxy groups;    -   A=boron, aluminum, gallium, indium, thallium, silicon,        germanium, tin, lead;    -   x=0 or 1 for B, Al, Ga, In, TI;    -   x=0 for Si, Ge, Sn, Pb;    -   in the case when x=0 and A=B, Al, Ga, In, Tl, then R⁴ is        omitted, or bringing them in contact with polymers containing        one or more of the elements B, Al, Ga, In, Tl, Si, Ge, Sn, Pb.

In contact with lithium, compounds with halogen bonds can be cleaved,forming lithium halide in part. The lithium halide may be deposited inthe coating layer because it is not soluble in the inerthydrocarbon-based solvent that is used, i.e., forming a lithium that mayalso contain lithium halide in its surface. When using such a powder ina lithium battery, which usually contains liquid electrolytes, which inturn contain polar organic solvents, the lithium halide dissolves andmay then come in contact with all battery components. It is known thatlithium halides, in particular LiCl, LiBr and LiI, have a corrosiveeffect on cathode current diverters made of aluminum. This attackshortens the calendar lifetime of the battery (see, for example, H. B.Han, J. Power Sources 196 (2011), 3623-32). In the case of housings orcurrent diverters made of aluminum, the use of lithium impressionstreated with halogen-free passivating agents is preferred.

The preferred lithium source is a pure grade, i.e., in particular agrade of lithium that has a very low sodium content. Such metal gradesare available commercially as “battery grade” lithium. The Na content ispreferably <200 ppm and especially preferably <100 ppm. It hassurprisingly been found that when using lithium metal of a low sodiumcontent, particularly stable products that can be handled safely can beproduced.

The reaction between the lithium metal and one or more of thepassivating agents according to the invention takes place in thetemperature range between 50 and 300° C., preferably between 100 and280° C. Molten lithium is most especially preferably used, i.e., thereaction temperature is at least 180.5° C. and spherical lithiumparticles (i.e., lithium powder or granules consisting of sphericalparticles) are produced and treated in the molten form with apassivating agent according to the invention.

In a most especially preferred production variant, the lithium is firstheated to a temperature above the melting point of lithium (180.5° C.)under an inert gas (noble gas, for example, dry argon) in an organicinert solvent or solvent mixture (usually hydrocarbon based). Thisprocess can take place at normal pressure when using solvents withboiling points >180° C. (for example, undecane, dodecane orcorresponding commercially available mineral oil mixtures, for example,Shellsols). On the other hand, if more readily volatile hydrocarbons,for example, hexane, heptane, octane, decane, toluene, ethylbenzene orcumene are used, then the melting process takes place in a closed vesselunder pressurized conditions.

After complete melting, an emulsion of the metal in hydrocarbon isprepared. Depending on the desired particle geometries (diameter), thisis accomplished by homogenization using agitating tools which yield therequired shearing forces for the respective impression. For example, ifa powder with particle sizes of less than 1 mm is to be prepared, adispersing disk may be used, for example. The precise dispersingparameters (i.e., mainly the rotational speed and dispersing time) willdepend on the desired particle size. These parameters also depend on theviscosity of the dispersing solvent as well as individual geometricparameters of the agitating element (e.g., diameter, exact position andsize of the teeth).

Those skilled in the art can easily determine how to fine tune, throughappropriate experiments, the dispersing process for preparing thedesired particle distribution.

If lithium particles in a grain size range between 5 and 100 pm are tobe produced, then the agitating frequency is generally between 1000 and25,000 revolutions per minute (rpm), preferably 2000 to 20,000 rpm. Thedispersing time, i.e., the period of time within which the dispersingtool runs at full capacity is between 1 and 60 minutes, preferably 2 and30 minutes. If particularly finely divided particles are desired, thenextremely high-speed special tools may be used, for example, it isavailable commercially under the brand name Ultraturrax.

The passivating agent may be added together with the metal and thesolvent before the start of the heating phase. However, the passivatingagent is preferably added only after melting the metal, i.e., attemperatures >180.5° C. This addition may take place in an uncontrolledmanner (i.e., in one portion) during the dispersion process, but thepassivating agent is preferably added over a period of time over approx.5 to 5000 sec, especially preferably 30 sec to 1000 sec.

Alternatively, the particle preparation can also be accomplished by anatomization process. In this case, molten lithium is sprayed into aninert gas atmosphere. After the resulting metal powder has cooled andsolidified, it can be dispersed in an inert organic solvent (usually ahydrocarbon) and reacted with one or more of the passivating agentsaccording to the invention at temperatures below the melting point oflithium.

Suitable passivating agents include the molecular or “at” compounds ofthe general formulas I or II or polymers containing elements of maingroups 3 and/or 4 of the periodic table of elements that can be alloyedwith lithium. Especially preferred compound are those of boron,aluminum, silicon and tin. Examples of particularly preferredpassivating agents include:

-   -   Boric acid esters of the general formula B(OR)₃,    -   Boron and aluminum halides B(Hal)₃ and/or Al(Hal)₃,    -   Lithium borates and aluminates of the formulas Li[B(OR)₄] and/or        Li[Al(OR)₄],    -   Aluminum alcoholates of the general formula Al(OR)₃,    -   Alkyl aluminum compounds of the general formula AlR_(3-n)Hal_(n)        (n=0, 1 or 2),    -   Silicon and tin halides Si(Hal)₄ and Sn(Hal)₄,    -   Silicic acid esters Si(OR)₄ and tin alcoholates Sn(OR)₄,    -   Disiloxanes and distannoxanes R₃Si—O—SiR₃ and R₃Sn—O—SnR₃,    -   Alkyl compounds of silicon and tin, SiR₄, SnR₄,    -   Mixed alkyl halogen compounds of silicon and tin        SiR_(4-n)Hal_(n) (n=1, 2 or 3) and/or SnR_(4-n)Hal_(n) (n=1, 2        or 3),    -   Mixed alkylalkoxy compounds of silicon and tin SiR_(4-n)(OR)_(n)        (n=1, 2 or 3) and/or SnR_(4-n)(OR)_(n) (n=1, 2 or 3),    -   Silicon-based polymers such as silicones (polyorganosiloxanes        such as R₃SiO[R₂SiO]_(n)SiR₃, e.g., poly(dimethylsiloxane)        where Hal=F, Cl, Br, I; R=alkyl, alkenyl or aryl radicals or two        radicals R together denote a 1,2-diolate (e.g.,        1,2-ethanediolate), a 1,2- or 1,3-dicarboxylate (e.g., oxalate        or malonate) or a 2-hydroxycarboxylate dianion (e.g.,        salicylate, glycolate or lactate).

The passivating agents, either in pure form or dissolved in a solventthat is inert with respect to lithium metal (i.e., hydrocarbons, forexample) or in a less reactive aprotic solvent (an ether, for example),are added to the mixture of lithium metal and the aprotic inert solvent.Addition of the passivating agent is followed by a post-reaction phase,during which the reaction is completed. The duration of thepost-reaction phase depends on the reaction temperature and thereactivity of the selected passivating agent with respect to lithiummetal. The average particle size of the metal powder according to theinvention is max. 5000 μm, preferably max. 1000 μm and especiallypreferably max. 300 μm.

However, the method according to the invention is also suitable forpassivation of nonspherical lithium metal impressions, for example,lithium foil. In this case, the passivation is performed with thefilm-forming precursors of main groups 3 and/or 4 of the periodic tableof elements at temperatures below the melting point of lithium.

In the sense of the present invention, it is also possible to perform amultistep passivation, in which at least once one or more of thepassivating agents according to the invention are used. For example,passivation may first be performed according to the prior art usingfatty acids or fatty acid esters and the resulting particulate lithiummetal can then be stabilized further by an additional coating with oneof the passivating agents according to the invention. This additionalpassivation is performed in a hydrocarbon solvent, preferably attemperature below the melting point of lithium (i.e., <180.5° C.).

The amount of passivating agent used for the surface coating depends onthe particle size, the chemical structure of the passivating agent andthe desired layer thickness. In general the molar ratio between Li metaland the passivating agent is 100:0.01 to 100:5, preferably 100:0.05 to100:1. In the case of polymeric passivating agents, the molar ratio iscalculated from the quotient of lithium and a single monomer unit. Forexample, in the case of poly(dimethyl)siloxane (monomer unit=(CH3)2SiO)an effective molecular weight is 74 g/mol.

When using the preferred amount of passivating agent, lithium metalproducts having contents >95% preferably >97% are the result.

The passivated lithium metal impression according to the inventionsurprisingly contains the alloy-forming element A at least partially inelemental form or in the form of an alloy with lithium. Silicon is thusformed in the reaction of the passivating agents containing siliconaccording to the invention with metallic lithium, forming in a secondstep the Li-rich alloy Li₂₁Si₅. It is assumed that metallic lithium isformed by a redox process by using silicic acid esters as follows, forexample:

Si(OR)₄+4Li→4LiOR+Si

In a second step the resulting metallic silicon forms one of the knowncrystalline Li alloys (mostly one of the existing alloys having thehighest lithium content, i.e., Li₂₁Si₅) in the case of Si. The lithiumalcoholate which is formed as a coupling product may react furtherdepending on the selected synthesis conditions, forming lithium oxide,for example. A multicomponent coating of the lithium impressionconsisting of an alloy layer and a salt-type layer containing Li isformed in this way.

Lithium metal powder that has a low sodium content and has beenpassivated according to the invention has surprisingly been proven to beparticularly stable in contact with reactive polar solvents, forexample, N-methyl-2-pyrrolidone.

The lithium metal powder according to the invention surprisingly doesnot have any significant exothermic effect in the DSC test in suspensionwith N-methyl-2-pyrrolidone (water content less than approx. 200 ppm)when stored for at least 15 hours at 50° C. and especially preferably at80° C. and in particular it does not exhibit any “runaway” phenomenon.This behavior will now be explained on the basis of the followingexamples.

The passivated lithium metal impressions according to the invention maybe used for prelithiation of electrochemically active materials, e.g.,graphite, alloy or conversion anodes for lithium batteries or after asuitable mechanical physicochemical pretreatment (pressing, mixing withbinder materials, etc.) for the production of metal anodes for lithiumbatteries.

The present invention will now be explained in greater detail below onthe basis of five examples and two illustrations without therebylimiting the claimed scope of the embodiments.

The product stability is determined by means of DSC (differentialscanning calorimetry). An apparatus from the Systag company inSwitzerland (the Radex system) was used. Approx. 2 g NMP and 0.1 glithium metal powder were weighed into the sample containers. Sampleswere stored for 15 hours at certain temperatures. The particle sizedistribution was determined using the Lasentec FBRM inline analyzer fromMettler-Toledo.

FIG. 1 shows an x-ray diffractogram of the metal powder from example 1,passivated with a layer containing Si

-   -   x: reflexes of lithium metal    -   o: reflexes of Li₂₁ Si₅

FIG. 2 shows an x-ray diffractogram of the metal powder from Example 2passivated with a layer containing Si

Example 1 Production of a Lithium Metal Powder Having a Low SodiumContent, Passivated with a Layer Containing Silicon (TetraethylSilicate, TEOS, as the Passivating Agent)

405 g Shellsol® D100 and 20.1 g lithium metal sections are placed in adry 2-liter stainless steel double-jacketed reactor equipped with adispersing agitator mechanism and inertized with argon. The lithium hasa sodium content of 40 ppm. While agitating gently (approx. 50 rpm), theinternal temperature is raised to 240° C. by jacket heating and a metalemulsion is produced by means of the disperser. Then 1.5 g TEOSdissolved in 10 mL Shellsol® D100 is added with a syringe within about 5minutes. During this addition, the suspension is agitated with a strongshearing action. Then the agitator is stopped and the suspension iscooled to room temperature.

The suspension is poured onto a glass suction filter. The filter residueis washed several times with hexane until free of oil and then vacuumdried.

Yield: 19.2 g (95% of the theoretical);

Average particle size: 140 pm (FBRM particle size analyzer fromMettler-Toledo);

Metal content: 99.5% (gas volumetric);

Stability in NMP, water content 167 ppm: stable for 15 hours at 80° C.;runaway reaction after 2.5 hours at 90° C.;

Si content: 0.40 wt %;

Surface analysis by XRD: phase components of Li₂₁Si₅

Example 2 Production of a Lithium Metal Powder with a Low SodiumContent, Passivated with a Layer Containing Silicon (VinylTriethoxysilane as the Passivating Agent)

415 g Shellsol® D100 and 98.4 g lithium metal sections are placed in adry 2-liter stainless steel double-jacketed reactor equipped with adispersing agitator mechanism and inertized with argon. The lithium hasa sodium content of 40 ppm. While agitating gently (approx. 50 rpm), theinternal temperature is raised to 240° C. by jacket heating and a metalemulsion is prepared by means of the disperser. Then 2.7 g vinyltriethoxysilane dissolved in 20 mL Shellsol® D100 is added with asyringe within about 5 minutes. During this addition, the suspension isagitated with a strong shearing action. Then the agitator is stopped andthe suspension is cooled to room temperature.

The suspension is poured onto a glass suction filter. The filter residueis washed several times with hexane until free of oil and then vacuumdried.

Yield: 95.2 g (97% of the theoretical);

Average particle size: 101 μm (FBRM particle size analyzer fromMettler-Toledo);

Metal content: 99.7% (gas volumetric);

Stability in NMP, water content 167 ppm: stable for 15 hours at 80° C.;a slightly exothermic reaction (no runaway phenomenon) after 2 hours at90° C.;

Si content: 0.26 wt %;

Surface analysis by XRD: very little phase amounts of Li₂₁Si₅

Example 3 Production of a Lithium Metal Powder with a Low SodiumContent, Passivated with a Layer Containing Silicon(Polydimethylsiloxane, PDMS as the Passivating Agent)

405 g Shellsol® D100 and 20.6 g lithium metal sections are placed in adry 2 liter stainless steel double-jacketed reactor equipped with adispersing agitator mechanism and inertized with argon. The lithium hasa sodium content of 40 ppm. While agitating gently (approx. 50 rpm), theinternal temperature is raised to 240° C. by jacket heating and a metalemulsion is prepared by means of the disperser. Then 3.3 gpolydimethylsiloxane (CAS no. 9016-00-6) is added with a syringe withinabout 3 minutes. During this addition, agitating is continued with astrong shearing action. Agitation is then continued for 30 minutes atabout 210° C., the agitator is then stopped and the suspension is cooledto room temperature.

The suspension is poured onto a glass suction filter. The filter residueis washed several times with hexane until free of oil and then vacuumdried.

Yield: 20.1 g (98% of the theoretical);

Average particle size: 51 μm (FBRM particle size analyzer fromMettler-Toledo);

Metal content: 99% (gas volumetric);

Stability in NMP, water content 167 ppm: stable for 15 hours at 80° C.,then runaway after a few minutes at 100° C.;

Si content: 0.70 wt %;

Example 4 Production of a Lithium Metal Powder with a Low SodiumContent, Passivated with a Layer Containing Boron (LithiumBis(Oxalate)Borate, LiBOB) as the Passivating Agent

396 g Shellsol® D100 and 19.1 g lithium metal sections are placed in adry 2 liter stainless steel double-jacketed reactor equipped with adispersing agitator mechanism and inertized with argon. The lithium hasa sodium content of 40 ppm. While agitating gently (approx. 50 rpm), theinternal temperature is raised to 210° C. by jacket heating and a metalemulsion is prepared by means of a disperser. Then 6.1 g of a 30%solution of LiBOB in THF is added with a syringe within about 4 minutes.During this addition, the suspension is agitated with a strong shearingaction. Next the agitator is stopped and the suspension is cooled toroom temperature.

The suspension is poured onto a glass suction filter. The filter residueis washed several times with hexane until free of oil and then vacuumdried.

Yield: 20.5 g (107% of the theoretical);

Average particle size: 43 μm (FBRM particle size analyzer fromMettler-Toledo);

Metal content: 96% (gas volumetric);

Stability in NMP, water content 167 ppm: stable for 15 hours at 80° C.;runaway after 4 hours at 100° C.;

Example 5 Production of a Lithium Metal Powder with a Low SodiumContent, Passivated by a Layer Containing Boron (Triisopropyl Borate asthe Passivating Agent)

435 g Shellsol® D100 and 19.6 g lithium metal sections are placed in adry 2 liter stainless steel double-jacketed reactor equipped with adispersing agitator mechanism and inertized with argon. The lithium hasa sodium content of 17 ppm. While agitating gently (approx. 50 rpm), theinternal temperature is raised to 210° C. by jacket heating and a metalemulsion is prepared by means of the disperser. Then 2.7 g triisopropylborate dissolved in 20 mL Shellsol® D100 is added with a syringe withinabout 10 minutes. During this addition, the emulsion is agitated with astrong shearing action. Next the agitator is stopped and the suspensionis cooled to room temperature.

The suspension is poured onto a glass suction filter. The filter residueis washed several times with hexane until free of oil and then vacuumdried.

Yield: 19.4 g (99% of the theoretical);

Average particle size: 125 μm (FBRM particle size analyzer fromMettler-Toledo);

Metal content: 97% (gas volumetric);

Stability in NMP, water content 167 ppm: stable for 15 hours at 80° C.;stable for 15 hours at 100° C.; runaway after a few minutes at 120° C.;

B content: 0.68 wt %;

1.-15. (canceled)
 16. A stabilized particulate lithium metal, wherein ithas a core of metallic lithium which is surrounded with an outerpassivating layer containing one or more elements of main groups 3and/or 4 of the periodic table of elements that can be alloyed withlithium.
 17. The stabilized particulate lithium metal of claim 16,wherein the element that can be alloyed with lithium and is present inthe outer layer is present in elemental form or as an alloy withlithium.
 18. The stabilized particulate lithium metal according to claim16 wherein it has a sodium content <200 ppm.
 19. The stabilizedparticulate lithium metal according to claim 17 wherein it has a sodiumcontent <200 ppm.
 20. The stabilized particulate lithium metal accordingto claim 16, wherein it has a sodium content <100 ppm.
 21. Thestabilized particulate lithium metal according to claim 17, wherein ithas a sodium content <100 ppm.
 22. The stabilized particulate lithiummetal according to claim 16, wherein it has a sodium content <50 ppm.23. The stabilized particulate lithium metal according to claim 17,wherein it has a sodium content <50 ppm.
 24. The stabilized particulatelithium metal according to claim 16, wherein at least one elementselected from B, AI, Ga, In, Tl, Si, Ge, Sn, Pb is present as theelement capable of being alloyed element.
 25. The stabilized particulatelithium metal according to claim 17, wherein at least one elementselected from B, Al, Ga, In, TI, Si, Ge, Sn, Pb is present as theelement capable of being alloyed element.
 26. The stabilized particulatelithium metal according to claim 16, wherein it has an average particlesize of max. 5000 μm.
 27. The stabilized particulate lithium metalaccording to claim 17, wherein it has an average particle size of max.5000 μm.
 28. The stabilized particulate lithium metal according to claim16, wherein it does not exhibit any exothermic effect.
 29. Thestabilized particulate lithium metal according to claim 28, wherein theexothermic effect is no runaway phenomenon in contact withN-methyl-2-pyrrolidone with a water content of approx. 200 ppm for atleast 15 hours at 50° C.
 30. A method for producing a stabilized lithiummetal 17, wherein lithium metal is brought in contact with film-formingprecursors containing elements of main groups 3 and 4 of the periodictable of elements at a temperature in the range between 50 and 300° C.in an inert organic solvent.
 31. The method according to claim 29,wherein the passivating agent is of formula I or formula II:[AR¹R²R³R⁴]Li_(x)  (I)or R¹R²R³A-O-AR⁴R⁵R⁶  (II) wherein R¹R²R³R⁴R⁵R⁶=independently of oneanother alkyl (C₁-C₁₂), aryl, alkoxy, aryloxy or halogen or two radicalsR together denote a 1,2-diolate, a 1,2- or 1,3-dicarboxylate or a2-hydroxycarboxylate dianion; radicals R¹ to R⁶ may contain additionalfunctional groups, A is selected from the group consisting of boron,aluminum, gallium, indium, thallium, silicon, germanium, tin and lead;wherein x is 0 or 1 when A is boron, aluminum, gallium, indium,thallium; and wherein x is 0 when A is silicon, germanium, tin or lead;and wherein when x is 0 and A is boron, aluminum, gallium, indium orthallium, then R⁴ is omitted, or polymers containing one or more of theelements B, Al, Ga, In, Tl, Si, Ge, Sn, Pb.
 32. The method according toclaim 29, wherein the molar ratio between Li metal and the passivatingagent is 100:0.01 to 100:5.
 33. The method according to any claim 29,wherein inert organic solvent is selected from the group consisting ofhexane, heptane, octane, decane, undecane, dodecane, toluene,ethylbenzene and cumene.
 34. The method according to claim 29, whereinan additional coating is performed at temperature <180.5° C.
 35. Themethod according to claim 29, wherein nonspherical lithium metalimpressions, for example, lithium foil are passivated at temperaturesbelow 180.5° C. with film-forming precursors according to the invention.36. A method comprising prelithiating an electrochemically activematerial with the stabilized particulate lithium metal according toclaim
 16. 37. An electrode comprising the stabilized particulate lithiummetal according to claim 16.